An apparatus for implementing the method referred to above for an air-fuel metering system is known, for example, from German published patent application DE-OS No. 2,847,021 and British patent application No. 2,034,930 which is a Convention application based on the German application.
These applications disclose in particular a mixture metering system in which the quantities metered are governed by so-called "learning control systems". In these "learning control system", stores values for the injection are stored in a read-only memory and transferred to a read-write memory on starting the internal combustion engine. These stores values serve for the pre-control of, for example, the quantity to be injected or of fuel metering generally. Subsequent thereto, individual characteristic field values can be corrected in dependence on operating characteristic quantities and can be written into the memory.
Depending on whether it is only individual values or entire characteristic field ranges that are adapted by means of the superposed control, various disadvantages result. If only individual values are adapted, the relevant characteristic field output quantity has to be adapted to its desired value by a control method at all operating points of the internal combustion engine which are predetermined by the input quantities. In this method, the fact that all individual output quantities have to be accessed for modification of the entire characteristic field does not prove to be a particular advantage. As a rule, a substantial amount of time elapses until the characteristic field is adapted to the new situation. In particular, in stored values broken up in very fine segments, it may then happen that some values are never or only very rarely accessed and consequently not adapted.
The other type of adaptation wherein a group of coherent characteristic field values is influenced by a common multiplicative or additive correction value permits only a very rough correction of individual characteristic field values. This method cannot perform an optimum characteristic field adaptation, particularly not if individual characteristic field values in the individual characteristic field ranges have a tendency to move in opposite directions.